Introduction

Bur oak is a huge tree reaching a height and spread of 70 to 90 feet and has an impressive crown, massive trunk, and stout branches. There is a specimen in Philadelphia which is about seven feet in diameter and over 90 feet wide. Bark is an unusual light brown to grey depending on the specimen, and is deeply furrowed on older trees. Young stems have corky ridges making them appear stout. Acorns are almost completely covered with a furry, bur-like cap and are large, creating a sizeable clean-up job in a maintained landscape. Young trees have an attractive, symmetrical, dense crown and they are well-suited for street tree planting. Architects like the tree due to its uniformity in crown shape.

Culture

Other

Roots: not a problem

Winter interest: no

Outstanding tree: yes

Ozone sensitivity: tolerant

Verticillium wilt susceptibility: resistant

Pest resistance: resistant to pests/diseases

Use and Management

Trees are well-suited for street, park and parking lot planting but enough soil space should be available to accommodate growth. This large oak should not be planted in tree lawn strips less than 10 feet wide. However, if soil is not compacted, roots usually stay below the soil surface and do not lift sidewalks or curbs.

This oak will adapt to various soils where other oaks sometimes fail but is difficult to transplant from well-drained soil due to the tap root. As with most trees grown in urban areas, the tap root becomes much less prominent as the tree grows older, giving way to a more shallow, horizontal root system. It is well-adapted to alkaline soils, poor drainage, high clay content, and is very drought-tolerant.

Propagation of oaks by seed is the most common.

Pests

No pests are normally serious.

Galls cause homeowners much concern. There are many types and galls can be on the leaves or twigs. Most galls are harmless so chemical controls are not suggested.

Scales of several types can usually be controlled with sprays of horticultural oil.

Aphids cause distorted growth and deposits of honeydew on lower leaves. On large trees, naturally-occurring predatory insects will often bring the aphid population under control.

Boring insects are most likely to attack weakened or stressed trees. Newly planted young trees may also be attacked. Keep trees as healthy as possible with regular fertilization and water during dry weather.

Many caterpillars (including gypsy moth) feed on oak. Large trees tolerate some feeding injury without harm. Trees repeatedly attacked, or having some other problem, may need spraying. Tent caterpillars form nests in trees then eat the foliage. The nests can be pruned out when small. Where they occur, gypsy moth caterpillars are extremely destructive on oaks.

Twig pruner causes twigs to drop off in the summer. The larvae ride the twig to the ground. Rake up and destroy fallen twigs. Fall cankerworm has been a problem in some years.

Leaf miners cause brown areas in leaves. To identify leaf miner injury tear the leaf in two across the injury. If the injury is due to leaf miner, upper and lower leaf surfaces are separate and black insect excrement will be seen.

Diseases

No diseases are normally serious. Bur oak is more or less resistant to oak wilt.

Anthracnose may be a serious problem in wet weather. Infected leaves have dead areas following the midrib or larger veins. These light brown blotches may run together and, in severe cases, cause leaf drop. Trees of low vigor, repeatedly defoliated, may die. Trees defoliated several years in a row may need spraying, to allow the tree to recover.

Leaf blister symptoms are round raised areas on the upper leaf surfaces causing depressions of the same shape and size on lower leaf surfaces. Infected areas are yellowish-white to yellowish-brown. The disease is most serious in wet seasons in the spring but it does not need to be treated.

A large number of fungi cause leaf spots but are usually not serious. Rake up and dispose of infected leaves.

Powdery mildew coats leaves with white powdery growth.

Shoestring root rot attacks the roots and once inside moves upward, killing the cambium. The leaves on infected trees are small, pale or yellowed and fall early. There is no practical control. Healthy trees may be more resistant than trees of low vigor.

Footnotes

1.

This document is ENH-709, one of a series of the Environmental Horticulture Department, UF/IFAS Extension. Original publication date November 1993. Revised December 2006. Reviewed February 2014. Visit the EDIS website at http://edis.ifas.ufl.edu.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.